FIELD OF THE INVENTION
The invention relates to a passive pulse generator and to a method for activating a safety fitting in a nuclear power plant.
In a nuclear power plant which is equipped, for example, with a pressurized or boiling water reactor, cold coolant is fed to and heated coolant is discharged from a reactor pressure vessel in a closed circuit in a reactor safety vessel. The coolant is heated by core processes taking place in the reactor pressure vessel. Heat energy that is absorbed at the same time by the coolant serves for generating electric energy. At the same time, the heated coolant is cooled through the use of heat exchange processes and is fed to the reactor pressure vessel again. A leak in that closed cooling circuit leads to a reduction in the coolant and therefore to a temperature rise in the reactor pressure vessel. A temperature rise in the reactor pressure vessel also leads automatically to a temperature rise, for example in a condensation chamber, to which the reactor pressure vessel is connected for safety reasons. At present, however, a small leak in the coolant circuit is not detected. Instead, the coolant loss which occurs is compensated automatically by regulating a filling level of the reactor pressure vessel from existing coolant reservoirs. However, should a major coolant loss incident occur, in that case the temperature in the reactor safety vessel would be increased by the amount of the temperature rise due to the leak.
Published French Patent Application 2 690 219 discloses a safety fuse which releases a valve when a temperature is exceeded. The disadvantage of a safety fuse is that it is available only once and, after use, has to be replaced by a new one.
Published UK Patent Application GB 2 209 200 A discloses a thermal closing valve that, particularly in the domestic sector, is used for fire protection reasons in gas lines in which an easily flammable or explosive gas flows. The closing valve closes the gas line reliably and permanently when a specific temperature is exceeded. For that purpose, a special spring is provided and closing of the gas line is brought about by thermal expansion of the spring in reaction to a temperature rise. The spring is specially constructed so that the gas line still remains closed even when the temperature falls again. The spring therefore does not return to its initial position in the event of a lowering of temperature. On the contrary, it has to be replaced by a new spring, in order to ensure that the closing valve is operative again.